Research And Insight

Disinfection

Disinfection is one of the most important processes in water treatment. This step eliminates microorganisms in drinking and process water to ensure safe water use according to relevant regulations and directives.

Water disinfection to remove microorganisms is essential, especially when the water is supplied from lakes and rivers etc.

Removal of pathogens
Rivers and lakes may contain high levels of pathogens as a result from inadequately or non-treated discharges. This also includes sewage, from combined sewer systems that discharge untreated sewage during rain storms.

Contaminated domestic water systems
However, domestic water systems supplied from ‘clean’ water wells are often also contaminated. As a result, most drinking water installations in commercial buildings are disinfected to prevent microbiological contamination, such as legionella, E. coli, etc.

Definition of disinfection
Disinfection is defined as elimination of 99.999% of germs in water or on surfaces. This can be achieved through different chemical or physical methods. However, each method has its pros and cons:

  • Chlorine is often used in the form of chlorine gas, as commercial hypochlorite solution or as electrolytic generated hypochlorite.
  • Chlorine dioxide solution needs to be generated onsite from chemicals but is more effective than chlorine/hypochlorite. Chlorine dioxide is able to remove bio film and is has a long residual effect. 
  • Ozone is a gas which is produced onsite from oxygen and solved in water. It is the most effective oxidant but with a very short half-life. This procedure offers no residual effect.
  • UV radiation with high intensity as non-chemical method kills most bacteria but is only effective within the UV chamber and has no residual effect.
  • Filtration removes bacteria which passes the filter. This method should be regarded as a gatekeeper as it has no residual effect.
  • Pasteurisation, although widespread in commercial buildings, it has only limited effect. It does not remove bio film, the effect on free bacteria is limited, and there is no residual effect.

Generation of by-products
During the disinfection process different by-products are generated as a result of the reaction with compounds in the treated water or from the disinfectant itself.

Limit values
Limit values have to be observed at all times. Limit values for most by-products are available in regulations, guidelines and standards which are often specific for different countries or applications.

Grundfos supplies chlorine dosing pumps using full-vacuum chlorine gas (Cl2) dosing systems (Vaccuperm), sodium hypochlorite (NaOCl) electro-chlorination systems (Selcoperm), and chlorine dioxide (ClO2) preparation and dosing systems (Oxiperm).